题干

下列有关PCR过程的叙述中不正确的是(    )

A:受热变性破坏的是DNA分子内碱基对之间的氢键,也可利用解旋酶实现

B:引物与单链相应互补序列结合是依靠碱基互补配对原则完成

C:延伸过程中需要DNA聚合酶、ATP、四种核糖核苷酸

D:PCR与细胞内DNA复制相比所需酶的最适温度较高

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C

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    One year my children came home from school asking where we were going on your summer vacation. It seemed that all the other kids were1 where they were spending the summer. I couldn't 2to take them anywhere but I didn't want to tell them that so I just said, “It's a surprise!” They were 3. That bought me a little more 4.

    I called several amusement 5to see if there was a half-price event during the summer but no such 6. I tried everything, with no success, so I called some of the other moms to find that most were in the same7that I was. We decided to8 something fun for our kids to do. We had a meeting, all five of us, and9 what is now called a “playcation”.

    One mother was a  10, so on Mondays the kids would all go to her house. They would play games using plants and11. They also planted vegetables and12 them grow over the summer.

    Another mother had Bible 13 on Tuesdays. She asked some questions about Bible. The kid who answered  14got a penny, which they all turned in at the end to buy their goodie bags(礼品袋).

    At our house on Wednesdays, I made an outdoor 15training with my spare tires. The kids also walked a balance beam and raced through large cardboard boxes taped together.

    On 16they had arts and crafts across the street. Fridays were17by a wonderful single dad with a metal detector(金属探测器)who took everyone out treasure18 .

    The summer was a big19 . Okay, it wasn't Disney World,20 the kids didn't miss anything. My son actually asked me, “Can we do this again next year?”